Electronic devices use radio-frequency (RF) signals to enable users to talk with friends, download information, share pictures, remotely control household devices, receive global positioning information, or listen to radio stations. These radio-frequency signals are analog signals, which can physically travel between electronic devices and transfer digitally encoded communication data. An electronic device uses an analog-to-digital converter to convert an analog signal to a digital signal, which enables the communication data to be extracted. The analog-to-digital converter performs the conversion by sampling the analog signal at some sampling frequency. Typically the sampling frequency is greater than twice a frequency of the analog signal (e.g., according to Nyquist's rate), which enables the analog signal to be accurately represented in a digital domain.
Sometimes, however, unwanted signals in the environment, also known as jammers, are detected by the electronic device and can interfere with a desired communication signal. Examples of jammers include other, unrelated signals that exist within an operating environment and harmonics or other spurious signals that are associated with the desired communication signal. If these jammers have a frequency that is greater than or equal to half the sampling frequency of the analog-to-digital converter, the jammers can decrease a dynamic range of the electronic device and cause aliasing in the analog-to-digital converter. Aliasing occurs if the analog-to-digital converter under-samples the jammer such that a resulting digital output cannot be used to reconstruct the jammer (e.g., the sampling frequency is less than or equal to twice the frequency of the jammer). Due to aliasing, a digital representation of the jammer includes a lower frequency, which can interfere with the desired communication signal.
Some communication system designs use rejection or filter circuitry to attenuate and reject the jammer. Depending on a strength of the jammer, however, this circuitry can become large in size, require a substantial amount power, or become too expensive. Other designs may increase the sampling rate of the analog-to-digital converter to prevent aliasing. High-sampling rates, however, require additional power and can increase design complexity of the analog-to-digital converter. Overall, it becomes challenging to design an electronic device that provides alias rejection while also conserving power and efficiently using the available space in the electronic device.